This invention provides an inertia or acceleration-responsive electric switch for closing the circuit from the battery to light emitting diodes of an electronic watch, especially a wrist watch. The switch closes when the watch is moved with a predetermined angular acceleration. In the preferred construction, the switch is oriented in the watch case in such a position that it is responsive to a turning movement of the wrist on which a wrist watch is worn; but not responsive to movement in the direction in which the forearm of the wearer extends or in any direction orthogonal to that direction.
The amount of acceleration necessary to operate the switch depends upon the weight of an inertia element incorporated into the switch and upon a spring or other means by which the switch is normally held in open position. It is desirable that the switch not close too easily because this will result in unintentional closing of the switch and unnecessary use of the battery.
The preferred embodiment of the invention includes elements in the electrical circuit of the watch for preventing the supply of power to the light emitting diodes when the switch closes momentarily for a period of time less than a predetermined minimum. For example, in the preferred construction the switch contact must be maintained for more than one hundredth of a second in order to have power supplied to the light emitting diodes.
Another feature of the preferred embodiment is the use of a buffer between the battery and the display power input to the light emitting electrodes for maintaining a supply of power to the light emitting diodes for a predetermined time after the switch opens. The purpose of this feature is to permit the time display to last long enough so that a person using the watch can reliably determine the time.
One of the outstanding features of the invention is that a person wearing the watch of this invention as a wrist watch can get a time display by a rapid turn of the wrist which is a normal movement not likely to attract attention. In many cases it would be embarrassing for a person to reach over and operate a switch on his wrist watch making it evident to others at a conference that he was wondering about the time.
Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.